Widder studies underwater light. From bacteria to sea cucumbers to shrimp and fish, and even a few species of sharks, more than 50 percent of deep-ocean animals use light to holler and flirt and fight. They carry glowing torches atop their heads. They vomit brightness. They smear light on their enemies. Bioluminescence, Widder believes, is the most common, and most eloquent, language on earth, and it’s informing fields from biomedicine to modern warfare to deep-sea exploration. Most recently, on a historic voyage off the coast of Japan, she used her bioluminescent bag of tricks to summon the most legendary sea creature of all: the giant squid.

Today we are hoping to see ostracods, seed-size bioluminescent crustaceans that emerge from shallow sea grass beds and coral reefs some 15 minutes after sunset to put on one of the most sophisticated light shows in nature. The males leave blobs of mucus and radiant chemicals behind them, which hang suspended like glowing ellipses. “The spacing of the dots is species-specific,” Widder explains. “A female knows that if she goes to the end of the right string, she’ll find a male of her species that she can mate with.” This luminous seduction is called the “string of pearls” phenomenon.

Sixty feet below the surface, the pilot steers toward the gnarled limestone labyrinth of a coral reef. A three-foot barracuda gives us the hairy eyeball. A lionfish bristles in our lights. (Because it’s an invasive species, Widder glares back.) The sub leapfrogs between landing pads of soft white sand. We see hog snapper and upside-down jellyfish and a striped sea cucumber. Magnificent sponges resemble egg cups, golf balls and chess pieces. Most flabbergasting are the colors: There are sorbet corals, emerald plates of algae, touches of lavender, banana and rose. Fish dash past in peach and platinum.